Frack Quakes? Can hydraulic fracturing really cause earthquakes?

An earthquake that measured 4.0 on the Richter scale occurred near Youngstown, Ohio on New Year's Eve. In the weeks before, several smaller earthquakes had occurred. Many journalists have erroneously reported that scientists and state officials believe that hydraulic fracturing might have caused the earthquake. Actually, the scientists and officials believe that the earthquake might have been caused by the operation of an injection disposal well, not by hydraulic fracturing. Injection disposal and hydraulic fracturing are two different processes. The journalists might have been confused by the fact that the disposal wells at issue happened to be used for disposal of wastewater from hydraulic fracturing operations, but that was mere coincidence. Injection disposal wells are used to dispose of a variety of fluids. Further, oil and gas operators sometimes dispose of fracturing wastewater by means other than underground injection.

Injection Wells

Underground injection wells are regulated under the Safe Drinking Water Act. The Environmental Protection Agency reports that about 550 to 800,000 underground injection wells exist in the United States. Some of these are used for underground storage of fluids, including natural gas and oil. For example, the Strategic Petroleum Reserve is an example of a facility that stores oil underground. But most underground injection wells are used for the underground disposal of waste fluids. An injection disposal well might be used for years, and may receive hundreds of million gallons of waste fluids.

For several decades, many geologists have believed that the operation of injection disposal wells can cause earthquakes in certain circumstances in areas that already are prone to earthquakes. Scientists refer to man-made earthquakes as examples of "induced seismicity." One of the best known examples arises from the United States Army's operation of an injection disposal well at the Rocky Mountain Arsenal in Colorado during the 1960s. The Army disposed of approximately 165 million gallons of waste fluids in the well from 1962 through 1966 at a depth of approximately 12,000 feet. The Army quit using the well in early 1966 because geologists believed that fluid injections at the site were the cause of a series of earthquakes.

More recently, researchers and officials have suggested that earthquakes occurring near the Dallas-Fort Worth airport in 2009 and a large number of mostly small earthquakes (an earthquake "swarm") near Guy, Arkansas in late 2010 through early 2011 might have been caused by injection disposal wells. In addition, geologists also studied the possibility that underground injection wells caused a series of earthquakes that occurred near Trinidad, Colorado in 2001, but they did not reach a definitive conclusion. Their report stated that circumstances "do not rule out the possibility of the Trinidad earthquakes being induced, but neither do they make a strong case for the Trinidad shocks being induced."

Geologists also believe that the injection of water for enhanced recovery operations can cause earthquakes, and their belief is supported by a study of earthquakes occurring near Rangely, Colorado in the 1970s.

Because the earthquakes that are suspected of being caused by human activity occur only where geological faults and the possibility of earthquakes already exist, scientists have difficulty definitively linking seismic activity to underground injections. But many geologists believe that evidence strongly supports the theory that human activity can induce earthquakes. The type of evidence geologists examine in evaluating whether earthquakes might have been caused by underground injections include the distance between an underground injection point and the epicenter of an earthquake, and the timing of earthquakes relative to injection activity. Geologists have suggested that society's use of underground injection disposal wells need not stop, and that risk can be minimized by halting or decreasing the rate of injections when particular injection wells are believed to have caused small earthquakes.

Hydraulic Fracturing

Geologists are less confident about a link between hydraulic fracturing and earthquakes than they are about a link between injection disposal wells and earthquakes. Part of the reason for this is that a much smaller amount of fluid typically is injected during hydraulic fracturing than is injected in underground disposal operations. Also, a hydraulic fracturing operation lasts for days, while an underground disposal well might operate for years. Nevertheless, some geologists believe that fracturing can cause earthquakes, though generally only very small quakes.

The Oklahoma Geological Survey recently produced a report that found a possible correlation between fracturing activity and a series of earthquakes in that state, but the correlation was not definitive. The report concluded that "uncertainties in the data make it impossible to say with a high degree of certainty whether or not these earthquakes were triggered by natural means or by the nearby hydraulic-fracturing operation." As noted by the U.S. Geological Survey, "[e]arthquakes are not unusual in Oklahoma." Thus, the earthquakes may have had a natural origin.

Another case study comes from Britain, where Caudrilla Resources was using hydraulic fracturing to produce natural gas from a shale formation in Lancashire. An earthquake that measured 2.3 on the Richter scale, occurred on April 1, 2011. Another quake, which measured 1.5 on the Richter scale, occurred on May 27, 2011. A group of experts from across Europe studied the two earthquakes. They concluded that it was "highly probable" that fracturing had caused the earthquakes, but that an "unusual combination of factors" that they said was unlikely to occur again had been necessary in order for fracturing to cause the earthquakes. They estimated that, in the unlikely event that the factors did recur, the "worst-case scenario" was an earthquake with a maximum strength of 3.0 on the Richter scale.

Concluding Thoughts and References for Additional Reading

Geologists generally accept the idea that human activity, including the operation of injection disposal wells, can cause earthquakes in certain circumstances in areas that already have geological faults and the possibility of earthquakes. Geologists have suggested that our society need not stop using injection disposal wells, and that any danger can be minimized by halting or slowing underground injections when small earthquakes begin to occur. It is not as widely accepted that hydraulic fracturing can cause earthquakes, but some geologists believe that hydraulic fracturing can cause small earthquakes in some circumstances.

Comments (2)

Just wondering about your statement that "Underground injection wells are regulated under the Safe Drinking Water Act."

If you go to the EPA's website you will see that underground sources of drinking water are supposed to be protected by the UIC program. Then you will see that injection wells used to store frack fluid are exempt by means of the Energy Policy Act of 2005. Could you please advise as to what is regulating hydraulic fracturing waste fluid that is injected into the ground? If I understand this correctly, it is not the SDWA.

Safe Drinking Water Act

Several statutes may be leveraged to protect water quality, but EPA’s central authority to protect drinking water is drawn from the Safe Drinking Water Act (SDWA). The protection of USDWs is focused in the Underground Injection Control (UIC) program, which regulates the subsurface emplacement of fluid. Congress provided for exclusions to UIC authority (SDWA § 1421(d)), however, with the most recent language added via the Energy Policy Act of 2005:

“The term ‘underground injection’ –

(A) means the subsurface emplacement of fluids by well injection; and
(B) excludes –
(i) the underground injection of natural gas for purposes of storage; and
(ii) the underground injection of fluids or propping agents (other than diesel fuels) pursuant to hydraulic fracturing operations related to oil, gas, or geothermal production activities.”
While the SDWA specifically excludes hydraulic fracturing from UIC regulation under SDWA § 1421 (d)(1), the use of diesel fuel during hydraulic fracturing is still regulated by the UIC program. Any service company that performs hydraulic fracturing using diesel fuel must receive prior authorization from the UIC program. Injection wells receiving diesel fuel as a hydraulic fracturing additive will be considered Class II wells by the UIC program. The UIC regulations can be found in Title 40 of the Code of Federal Regulations Parts 144-148. State oil and gas agencies may have additional regulations for hydraulic fracturing. In addition, states or EPA have authority under the Clean Water Act to regulate discharge of produced waters from hydraulic fracturing operations.

Underground injection disposal wells are used to dispose of a wide variety of liquid substances, including wastewater from hydraulic fracturing. Such wells are regulated by the Safe Drinking Water Act even if they are used to dispose of wastewater from hydraulic fracturing.

The provision you reference from the 2005 Energy Policy Act concerns the process of hydraulically fracturing oil and gas wells, rather than to the use of injection wells to dispose of wastewater from hydraulic fracturing.

The critical distinction is between the process of hydraulic fracturing and the subsequent disposal of fracturing fluids. In hydraulic fracturing, a fluid is used to impose high pressure on an underground rock formation that contains oil or gas trapped in pore spaces. This fractures the rock and frees the oil or gas from the pores. After the fracturing process is complete, most of the water is recovered (the recovered water is called "flowback"). Then, the production of oil or gas begins. The flowback water often is disposed of using underground injection disposal wells.

The Safe Drinking Water Act was enacted in 1974. For many years, under both Republican and Democrat administrations, the EPA took the position that the Safe Drinking Water Act did not apply to the process of hydraulically fracturing oil and gas wells, but that the Act did apply to the subsequent disposal of fracturing wastewater. In 1997, the United States Eleventh Circuit (which oversees federal district courts in Alabama, Florida, and Georgia) ruled that the Act both to the process of hydraulically fracturing of oil and gas wells and to the subsequent disposal of flowback. The EPA accepted that ruling within the three states covered by the 11th Circuit, but otherwise stuck to its position that the Safe Drinking Water Act did not apply to the process of hydraulically fracturing of oil and gas wells.

The 2005 Energy Policy Act clarified the issue and reached a compromise by providing that the Safe Drinking Water Act will apply to the process of hydraulic fracturing oil or gas wells whenever diesel is used as part of the fracturing fluid mixture, but that the Safe Drinking Water Act otherwise does not apply.

The specifics of that compromise were based on what was going on at the time (which I'd be happy to elaborate on if you'd like), and arguably made sense based on what was occurring at that time, though some environmentalists wanted the SDWA to apply to all hydraulic fracturing and I suspect some in industry probably preferred the EPA's prior position that SDWA did not apply whatsoever to the process of hydrulic fracturing itself (even if diesel was used), though it did apply to the subsequent disposal of fracturing fluid.

In short, the disposal of hydraulic fracturing wastewater via underground injection is governed by the Safe Drinking Water Act.